Regular Expression Example 2 in theory of automata

Write the Regular expression for the language of all consecutive even length a’s ?

Accepted Strings: 

These all strings are the part of the language so should be accepted by regular expression;

Example strings = {aa, aab, aabaa, aabbaa, aabbbaa,………}and all other strings that contains consecutive even a’s.

Rejected Strings:

These all strings are not part of the language so should be rejected by regular expression;

Example strings = {a, b, ab, ba, aba, bba, abba,……………..} and all other strings that does not contains consecutive even a’s in strings.

R.E =  (aa+b)*

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